Childhood obesity is considered one of the most serious health problems facing youth. It is generally agreed that parents, as the gatekeepers to food and primary role models for children play an important role in shaping child eating behaviors. Unfortunately, little longitudinal data are available that examine simultaneously the evolution of parental feeding practices and child eating behaviors. The Net-Works grant is an NICHD-funded study that will follow parent feeding practices and child eating behaviors over time in the context of a multi- setting intervention trial (e.g., primary care, parenting classes, n-home visitors) targeting obesity prevention in low income and ethnically diverse children (n=500) ages two to four years. The present research proposal, Sib- Works, is ancillary to the Net-Works study and has two main aims. The primary aim of Sib-Works is to examine parent feeding practices in response to sibling dyads' eating behaviors and to identify reciprocal processes between sibling dyads' eating behaviors and parent feeding behaviors. For example, (1) How similar (or different) are eating behaviors of sibling dyads?; (2) What feeding practices do parents use if sibling dyads differ in their eating behaviors or Body Mass Index z-score (BMIz)?; (3) Do parents' tailor feeding behaviors to individual children's eating behaviors, or do they use feeding behaviors that have been established with older siblings?; (4) How does parent response to differences between children's eating behaviors affect the family food environment and family eating patterns? (5) What is the temporal relationship between parent feeding practices, sibling dyad's eating behaviors and sibling dyad's BMIz? Prior research has not examined the eating behaviors of more than one child in the same home. Thus, the current study offers a unique opportunity to expand knowledge of family dynamics related to obesity risk development. The secondary aim of Sib-Works is to examine intervention spillover effects of the NET-Works intervention on siblings. While some family-based studies have shown intervention spillover effects for family members of index participants, spillover effects have not been identified for childhood obesity interventions specifically. The Sib-Works main aims will be answered by adding measures to the parent study including: parent feeding practices (e.g., encouragement to eat more or less) with a sibling, sibling eating behaviors (e.g., interest in food), and family eating patterns (e.g., family meals). Sibling (closet-aged older sibling; n=317) data collection will coincide with the parent study at 12-, 24-, and 36-months. Sib-Works will allow for the evaluation of a more complex interactive model of the dynamics between parents and multiple children within the home food environment in order to identify key modifiable variables and processes that could be targeted in family-based interventions to prevent childhood obesity. Additionally, identifying whether interventions have the potential to impact siblings not directly participating in an intervention will inform whether programs need to be tailored to different children within the home, or whether universal interventions are adequate, thus reducing costs.